1. Field of the invention
The present invention concerns high-voltage and medium-voltage circuit breakers using a dielectric gas such as sulfur hexafluoride at a pressure of a few bars.
2. Description of the prior art
The invention is more particularly directed to a circuit breaker of the aforementioned type in which the increased pressure due to the appearance of an electric arc between the arc contacts at the time of tripping is exploited to apply a motive force to the mobile assembly; this arrangement, which is known, for example, from French patent No. 2 576 142, enables the arc to be extinguished without using an excessively high powered operating device.
In so-called low operating energy circuit breakers the increased pressure that originates near the arc propagates to the piston coupled to the mobile assembly.
The ease and speed with which the pressure is propagated depend partly on the obstacles to the flow of gas between the arc area and the piston and partly on the changing pressure gradient between the arc area and the face of the piston.
In known devices, for example as disclosed in the German published patent application DE 31 32825 A1 or in U.S. Pat. No. 2 957 063, the gas propagates in annular conduits the narrow cross-section of which is not favorable to high-speed flow; what is more, the pressure gradient between the arc area and the face of the piston decreases very rapidly so that the mechanical action of the gas is very soon attenuated after the arc appears.
One object of the invention is to provide a circuit breaker in which the pressure is rapidly transmitted to the piston coupled to the operating member and in which the flow of gas from the arc area occurs at high speed and without disturbance.